1. Field of the Invention
The present invention relates to a method for forming a silicon carbide(SiC) film preferably employed in an amorphous solar cell or the like.
2. Description of the Prior Art
Conventionally a silicon carbide(SiC) film has been formed by radio-frequency(rf) glow discharge method.
The rf glow discharge method has the virtue of being formable a uniform film over a large area, which is required for the solar cell.
However, characteristics of the obtained SiC film are low since the film-forming conditions such as the flow ratio of a material gas and the rf power density are not proper. And even by doping the obtained SiC film with boron for improving the characteristics thereof, the obtained dark-conductivity is only about 10.sup.-5 through 10.sup.-8 Scm.sup.-1 at the optical energy gap Eg of about 2.0 eV.
The SiC film employed in the amorphous solar cell is desired to have a wide optical energy gap in addition to a high dark-conductivity. However, the dark-conductivity tends to be lowered as the optical energy gap is increased. And at the optical energy gap of around 2.1 eV, the obtained dark-conductivity is only not more than 10.sup.-7 Scm.sup.-1.
In the case that the p-type amorphous SiC(a-SiC) film formed by the conventional method is employed in a window layer of a p-i-n type amorphous silicon solar cell, there arise problems that photo-electric current generated in an i layer due to the solar radiation cannot be effectively delivered to an external electrode because of low conductivity, and that solar radiation entering the solar cell is absorbed by the window layer (p layer) because of narrow optical energy gap thereof so as not to effectively reach an electrically generating layer (i layer).